QJSManagedValue Class
QJSManagedValue represents a value on the JavaScript heap belonging to a QJSEngine. More...
| Header: | #include <QJSManagedValue> |
| CMake: | find_package(Qt6 REQUIRED COMPONENTS Qml) target_link_libraries(mytarget PRIVATE Qt6::Qml) |
| qmake: | QT += qml |
| Since: | Qt 6.1 |
Public Types
| enum | Type { Undefined, Boolean, Number, String, Object, …, Function } |
Public Functions
| QJSManagedValue() | |
| QJSManagedValue(QJSValue value, QJSEngine *engine) | |
| QJSManagedValue(const QJSPrimitiveValue &value, QJSEngine *engine) | |
| QJSManagedValue(const QVariant &variant, QJSEngine *engine) | |
| QJSManagedValue(const QString &string, QJSEngine *engine) | |
| QJSManagedValue(QJSManagedValue &&other) | |
| ~QJSManagedValue() | |
| QJSValue | call(const QJSValueList &arguments = {}) const |
| QJSValue | callAsConstructor(const QJSValueList &arguments = {}) const |
| QJSValue | callWithInstance(const QJSValue &instance, const QJSValueList &arguments = {}) const |
| bool | deleteProperty(const QString &name) |
| bool | deleteProperty(quint32 arrayIndex) |
| QJSEngine * | engine() const |
| bool | equals(const QJSManagedValue &other) const |
| bool | hasOwnProperty(const QString &name) const |
| bool | hasOwnProperty(quint32 arrayIndex) const |
| bool | hasProperty(const QString &name) const |
| bool | hasProperty(quint32 arrayIndex) const |
| bool | isArray() const |
| bool | isBoolean() const |
| bool | isDate() const |
| bool | isError() const |
| bool | isFunction() const |
| bool | isInteger() const |
| bool | isNull() const |
| bool | isNumber() const |
| bool | isObject() const |
| bool | isQMetaObject() const |
| bool | isQObject() const |
| bool | isRegularExpression() const |
| bool | isString() const |
| bool | isSymbol() const |
| bool | isUndefined() const |
| bool | isUrl() const |
| bool | isVariant() const |
| QJSValue | property(const QString &name) const |
| QJSValue | property(quint32 arrayIndex) const |
| QJSManagedValue | prototype() const |
| void | setProperty(const QString &name, const QJSValue &value) |
| void | setProperty(quint32 arrayIndex, const QJSValue &value) |
| void | setPrototype(const QJSManagedValue &prototype) |
| bool | strictlyEquals(const QJSManagedValue &other) const |
| bool | toBoolean() const |
| QDateTime | toDateTime() const |
| int | toInteger() const |
| QJSValue | toJSValue() const |
| double | toNumber() const |
| QJSPrimitiveValue | toPrimitive() const |
| const QMetaObject * | toQMetaObject() const |
| QObject * | toQObject() const |
| QRegularExpression | toRegularExpression() const |
| QString | toString() const |
| QUrl | toUrl() const |
| QVariant | toVariant() const |
| QJSManagedValue::Type | type() const |
| QJSManagedValue & | operator=(QJSManagedValue &&other) |
Detailed Description
The QJSManagedValue class allows interaction with JavaScript values in most ways you can interact with them from JavaScript itself. You can get and set properties and prototypes, and you can access arrays. Additionally, you can transform the value into the Qt counterparts of JavaScript objects. For example, a Url object may be transformed into a QUrl.
A QJSManagedValue is always bound to a particular QJSEngine. You cannot use it independently. This means that you cannot have a QJSManagedValue from one engine be a property or a proptotype of a QJSManagedValue from a different engine.
In contrast to QJSValue, almost all values held by QJSManagedValue live on the JavaScript heap. There is no inline or unmanaged storage. Therefore, you can get the prototype of a primitive value, and you can get the length property of a string.
Only default-constructed or moved-from QJSManagedValues do not hold a value on the JavaScript heap. They represent undefined, which doesn't have any properties or prototypes.
Also in contrast to QJSValue, QJSManagedValue does not catch any JavaScript exceptions. If an operation on a QJSManagedValue causes an error, it will generally return an undefined value and QJSEngine::hasError() will return true afterwards. You can then catch the exception using QJSEngine::catchError(), or pass it up the stack, at your own discretion.
Note: As the reference to the value on the JavaScript heap has to be freed on destruction, you cannot move a QJSManagedValue to a different thread. The destruction would take place in the new thread, which would create a race condition with the garbage collector on the original thread. This also means that you cannot hold a QJSManagedValue beyond the lifespan of its engine.
The recommended way of working with a QJSManagedValue is creating it on the stack, possibly by moving a QJSValue and adding an engine, then performing the necessary operations on it, and finally moving it back into a QJSValue for storage. Moving between QJSManagedValue and QJSValue is fast.
Member Type Documentation
enum QJSManagedValue::Type
This enum represents the JavaScript native types, as specified by ECMA-262.
| Constant | Value | Description |
|---|---|---|
QJSManagedValue::Undefined | 0 | The undefined type |
QJSManagedValue::Boolean | 1 | The boolean type |
QJSManagedValue::Number | 2 | The number type |
QJSManagedValue::String | 3 | The string type |
QJSManagedValue::Object | 4 | The object type |
QJSManagedValue::Symbol | 5 | The symbol type |
QJSManagedValue::Function | 6 | The function type |
Note that the null value is not a type of itself but rather a special kind of object. You can query a QJSManagedValue for this condition using the isNull() method. Furthermore, JavaScript has no integer type, but it knows a special treatment of numbers in preparation for integer only operations. You can query a QJSManagedValue to find out whether it holds the result of such a treatment by using the isInteger() method.
Member Function Documentation
[constexpr noexcept] QJSManagedValue::QJSManagedValue()
Creates a QJSManagedValue that represents the JavaScript undefined value. This is the only value not stored on the JavaScript heap. Calling engine() on a default-constructed QJSManagedValue will return nullptr.
QJSManagedValue::QJSManagedValue(QJSValue value, QJSEngine *engine)
Creates a QJSManagedValue from value, using the heap of engine. If value is itself managed and the engine it belongs to is not engine, the result is an undefined value, and a warning is generated.
QJSManagedValue::QJSManagedValue(const QJSPrimitiveValue &value, QJSEngine *engine)
Creates a QJSManagedValue from value using the heap of engine.
QJSManagedValue::QJSManagedValue(const QVariant &variant, QJSEngine *engine)
Creates a QJSManagedValue from variant using the heap of engine.
QJSManagedValue::QJSManagedValue(const QString &string, QJSEngine *engine)
Creates a QJSManagedValue from string using the heap of engine.
QJSManagedValue::QJSManagedValue(QJSManagedValue &&other)
Move-constructs a QJSManagedValue from other. This leaves other in the default-constructed state where it represents undefined and does not belong to any engine.
[noexcept] QJSManagedValue::~QJSManagedValue()
Destroys the QJSManagedValue.
Note: This frees the memory slot it holds on the JavaScript heap. You must not destroy a QJSManagedValue from a different thread than the one where the QJSEngine it belongs to lives.
QJSValue QJSManagedValue::call(const QJSValueList &arguments = {}) const
If this QJSManagedValue represents a JavaScript FunctionObject, calls it with the given arguments, and returns the result. Otherwise returns a JavaScript undefined value.
The arguments have to be either primitive values or belong to the same QJSEngine as this QJSManagedValue. Otherwise the call is not carried out and a JavaScript undefined value is returned.
QJSValue QJSManagedValue::callAsConstructor(const QJSValueList &arguments = {}) const
If this QJSManagedValue represents a JavaScript FunctionObject, calls it as constructor with the given arguments, and returns the result. Otherwise returns a JavaScript undefined value.
The arguments have to be either primitive values or belong to the same QJSEngine as this QJSManagedValue. Otherwise the call is not carried out and a JavaScript undefined value is returned.
QJSValue QJSManagedValue::callWithInstance(const QJSValue &instance, const QJSValueList &arguments = {}) const
If this QJSManagedValue represents a JavaScript FunctionObject, calls it on instance with the given arguments, and returns the result. Otherwise returns a JavaScript undefined value.
The arguments and the instance have to be either primitive values or belong to the same QJSEngine as this QJSManagedValue. Otherwise the call is not carried out and a JavaScript undefined value is returned.
bool QJSManagedValue::deleteProperty(const QString &name)
Deletes the property name from this QJSManagedValue. Returns true if the deletion succeeded, or false otherwise.
bool QJSManagedValue::deleteProperty(quint32 arrayIndex)
Deletes the value stored at arrayIndex from this QJSManagedValue. Returns true if the deletion succeeded, or false otherwise.
QJSEngine *QJSManagedValue::engine() const
Returns the QJSEngine this QJSManagedValue belongs to. Mind that the engine is always valid, unless the QJSManagedValue is default-constructed or moved from. In the latter case a nullptr is returned.
bool QJSManagedValue::equals(const QJSManagedValue &other) const
Invokes the JavaScript '==' operator on this QJSManagedValue and other, and returns the result.
See also strictlyEquals.
bool QJSManagedValue::hasOwnProperty(const QString &name) const
Returns true if this QJSManagedValue has a property name, otherwise returns false. The properties of the prototype chain are not considered.
bool QJSManagedValue::hasOwnProperty(quint32 arrayIndex) const
Returns true if this QJSManagedValue has an array index arrayIndex, otherwise returns false. The properties of the prototype chain are not considered.
bool QJSManagedValue::hasProperty(const QString &name) const
Returns true if this QJSManagedValue has a property name, otherwise returns false. The properties of the prototype chain are considered.
bool QJSManagedValue::hasProperty(quint32 arrayIndex) const
Returns true if this QJSManagedValue has an array index arrayIndex, otherwise returns false. The properties of the prototype chain are considered.
bool QJSManagedValue::isArray() const
Returns true if this value represents a JavaScript Array object, or false otherwise.
bool QJSManagedValue::isBoolean() const
Returns true if the type of this QJSManagedValue is boolean, or false otherwise.
bool QJSManagedValue::isDate() const
Returns true if this value represents a JavaScript Date object, or false otherwise.
bool QJSManagedValue::isError() const
Returns true if this value represents a JavaScript Error object, or false otherwise.
bool QJSManagedValue::isFunction() const
Returns true if the type of this QJSManagedValue is function, false otherwise.
bool QJSManagedValue::isInteger() const
Returns true if this QJSManagedValue holds an integer value, or false otherwise. The storage format of a number does not affect the result of any operations performed on it, but if an integer is stored, many operations are faster.
bool QJSManagedValue::isNull() const
Returns true if this QJSManagedValue holds the JavaScript null value, or false otherwise.
bool QJSManagedValue::isNumber() const
Returns true if the type of this QJSManagedValue is number, or false otherwise.
bool QJSManagedValue::isObject() const
Returns true if the type of this QJSManagedValue is object, or false otherwise.
bool QJSManagedValue::isQMetaObject() const
Returns true if this value represents a QMetaObject pointer managed on the JavaScript heap, or false otherwise.
bool QJSManagedValue::isQObject() const
Returns true if this value represents a QObject pointer managed on the JavaScript heap, or false otherwise.
bool QJSManagedValue::isRegularExpression() const
Returns true if this value represents a JavaScript regular expression object, or false otherwise.
bool QJSManagedValue::isString() const
Returns true if the type of this QJSManagedValue is string, or false otherwise.
bool QJSManagedValue::isSymbol() const
Returns true if the type of this QJSManagedValue is symbol, or false otherwise.
bool QJSManagedValue::isUndefined() const
Returns true if the type of this QJSManagedValue is undefined, or false otherwise.
bool QJSManagedValue::isUrl() const
Returns true if this value represents a JavaScript Url object, or false otherwise.
bool QJSManagedValue::isVariant() const
Returns true if this value represents a QVariant managed on the JavaScript heap, or false otherwise.
QJSValue QJSManagedValue::property(const QString &name) const
Returns the property name of this QJSManagedValue. The prototype chain is searched if the property is not found on the actual object.
See also setProperty().
QJSValue QJSManagedValue::property(quint32 arrayIndex) const
Returns the property stored at arrayIndex of this QJSManagedValue. The prototype chain is searched if the property is not found on the actual object.
QJSManagedValue QJSManagedValue::prototype() const
Returns the prototype for this QJSManagedValue. This works on any value. You can, for example retrieve the JavaScript boolean prototype from a boolean value.
See also setPrototype().
void QJSManagedValue::setProperty(const QString &name, const QJSValue &value)
Sets the property name to value on this QJSManagedValue. This can only be done on JavaScript values of type object. Furhermore, value has to be either a primitive or belong to the same engine as this value.
See also property().
void QJSManagedValue::setProperty(quint32 arrayIndex, const QJSValue &value)
Stores the value at arrayIndex in this QJSManagedValue. This can only be done on JavaScript values of type object, and it's not recommended if the value is not an array. Furhermore, value has to be either a primitive or belong to the same engine as this value.
void QJSManagedValue::setPrototype(const QJSManagedValue &prototype)
Sets the prototype of this QJSManagedValue to prototype. A precondition is that prototype belongs to the same QJSEngine as this QJSManagedValue and is an object (including null). Furthermore, this QJSManagedValue has to be an object (excluding null), too, and you cannot create prototype cycles.
See also prototype().
bool QJSManagedValue::strictlyEquals(const QJSManagedValue &other) const
Invokes the JavaScript '===' operator on this QJSManagedValue and other, and returns the result.
See also equals.
bool QJSManagedValue::toBoolean() const
Converts the manged value to a boolean. If the managed value holds a boolean, that one is returned. Otherwise a boolean coercion by JavaScript rules is performed.
QDateTime QJSManagedValue::toDateTime() const
If this QJSManagedValue holds a JavaScript Date object, returns an equivalent QDateTime. Otherwise returns an invalid one.
int QJSManagedValue::toInteger() const
Converts the manged value to an integer. This first converts the value to a number by the rules of toNumber(), and then clamps it into the integer range by the rules given for coercing the arguments to JavaScript bit shift operators into 32bit integers.
Internally, the value may already be stored as an integer, in which case a fast path is taken.
Note: Conversion of a managed value to a number can throw an exception. In particular, symbols cannot be coerced into numbers, or a custom valueOf() method may throw. In this case the result is 0 and the engine carries an error after the conversion.
Note: The JavaScript rules for coercing numbers into 32bit integers are unintuitive.
QJSValue QJSManagedValue::toJSValue() const
Copies this QJSManagedValue into a new QJSValue. This is less efficient than move-constructing a QJSValue from a QJSManagedValue, but retains the QJSManagedValue.
double QJSManagedValue::toNumber() const
Converts the manged value to a number. If the managed value holds a number, that one is returned. Otherwise a number coercion by JavaScript rules is performed.
Note: Conversion of a managed value to a number can throw an exception. In particular, symbols cannot be coerced into numbers, or a custom valueOf() method may throw. In this case the result is 0 and the engine carries an error after the conversion.
QJSPrimitiveValue QJSManagedValue::toPrimitive() const
Converts the manged value to a QJSPrimitiveValue. If the managed value holds a type supported by QJSPrimitiveValue, the value is copied. Otherwise the value is converted to a string, and the string is stored in QJSPrimitiveValue.
Note: Conversion of a managed value to a string can throw an exception. In particular, symbols cannot be coerced into strings, or a custom toString() method may throw. In this case the result is the undefined value and the engine carries an error after the conversion.
const QMetaObject *QJSManagedValue::toQMetaObject() const
If this QJSManagedValue holds a QMetaObject pointer, returns it. Otherwise returns nullptr.
QObject *QJSManagedValue::toQObject() const
If this QJSManagedValue holds a QObject pointer, returns it. Otherwise returns nullptr.
QRegularExpression QJSManagedValue::toRegularExpression() const
If this QJSManagedValue holds a JavaScript regular expression object, returns an equivalent QRegularExpression. Otherwise returns an invalid one.
QString QJSManagedValue::toString() const
Converts the manged value to a string. If the managed value holds a string, that one is returned. Otherwise a string coercion by JavaScript rules is performed.
Note: Conversion of a managed value to a string can throw an exception. In particular, symbols cannot be coerced into strings, or a custom toString() method may throw. In this case the result is an empty string and the engine carries an error after the conversion.
QUrl QJSManagedValue::toUrl() const
If this QJSManagedValue holds a JavaScript Url object, returns an equivalent QUrl. Otherwise returns an invalid one.
QVariant QJSManagedValue::toVariant() const
Copies this QJSManagedValue into a new QVariant. This also creates a useful QVariant if QJSManagedValue::isVariant() returns false. QVariant can hold all types supported by QJSManagedValue.
QJSManagedValue::Type QJSManagedValue::type() const
Returns the JavaScript type of this QJSManagedValue.
QJSManagedValue &QJSManagedValue::operator=(QJSManagedValue &&other)
Move-assigns a QJSManagedValue from other. This leaves other in the default-constructed state where it represents undefined and does not belong to any engine.
Note: This frees the memory slot this QJSManagedValue holds on the JavaScript heap. You must not move-assign a QJSManagedValue on a different thread than the one where the QJSEngine it belongs to lives.